As described in JP-A-2004-272532, a memory medium such as a hard disk drive, which is rewritable, is used in an in-vehicle navigation device. The memory medium stores map data and the like.
Regarding the map data, periodically, new map data is formed so as to update new road information. When the map data in the navigation device is updated to new version map data, the new version map data is overwritten in a storing region of old version map data in the memory medium such as the hard disk drive, which is rewritable. As a result, the old version map data is replaced to the new version map data, and therefore the old version map data is deleted from the memory medium.
However, when the old version map data is deleted, it is difficult to revive the old version map data if a certain bug is found in the new version map data.
Further, for example, when the map data provides a large area map such as the European map, the large area to be covered with the map is divided into multiple regions. Then, the map data is also divided into multiple portions, each of which corresponds to a respective region. In this case, when a location is searched in the map, it is possible to reduce the number of object data. Accordingly, a process time for searching the location is reduced.
However, when the region is switched to another region, and a map data version of the original region is different from a map data version of a new region, it may be necessary to rewrite a whole of the map data stored in the memory medium from the map data of the original region to the map data of the new region. In this case, it is not convenient for the user.